Impact of High-Dose Sodium Supplementation on Cardiovascular and Thermoregulatory Responses

Proper sodium intake can help maintain plasma sodium levels, prevent plasma volume reduction, and improve performance, but specific guidelines on high dosages remain unclear. PURPOSE: The purpose of this study was to investigate the effect of a large dose sodium supplement before submaximal cycling on cardiovascular and thermoregulatory responses in a hot and humid environment. METHODS: Nine participants (6 males, 3 females; age = 22.22 ± 1.99 yrs; weight=79.93 ± 18.78 kg) completed both trials. Using a randomized, crossover design, participants consumed no supplement (control) at one trial and one with a large-dose sodium supplement (experimental, 810mg sodium/serving). After mixing the supplement in 532ml of water, participants drank 266ml 1 hour before the trial; consuming the rest within the first hour of cycling. During each visit, subjects cycled for 2-hours, maintaining their heart rate (HR) between 55-65% of their heart rate reserve in an environmental chamber set to 38°C and 60% relative humidity. Pre-, every 30-minutes during, and post-exercise, HR (bpm), blood pressure (mean arterial pressure [MAP]), and core temperature (Tc; °C). Repeated measures ANOVA were used to analyze differences between condition and time. Descriptive statistics (mean ± standard deviation) were calculated for all data. Significance level was set at p<05. RESULTS: Between conditions, there were no significant differences found (p>0.05) for any variables. No significant differences for any time point occurred for Tc. For time, pre-HR was significantly lower than all time-points during exercise (p<0.001). Pre-MAP was significantly lower than 30- (p=0.001), 60- (p=0.022), 90- (p=0.007), and 120-min (p=0.020) MAP. Pre-exercise average MAP in the supplement group was 88.65±6.27 and 88.17±4.94 in the control. 30-minutes into cycling, average MAP in the supplement group was 105.11 ± 8.84 vs. 101.7 ± 7.62 mmHg (control); 60min: experimental: 97.67 ± 5.91, control: 102.67 ± 10.17; 90min: experimental: 102.44 ± 11.04, control: 101.14 ± 8.43; and 120min: experimental: 98.68 ± 9.78, control: 100.17 ± 8.18 mmHg. CONCLUSION: A large dose sodium supplement consumed 1 hour before and during the first hour of exercise, does not negatively effect cardiovascular and thermoregulatory responses in recreationally trained adults.